While Online Communities (OCs) are increasingly used to involve people in organizations and societies, few studies focus on how OC influence political decision making within eParticipation initiatives. This issue is explored through an interpretive case-study of the Italian Five Star Movement (M5S), a mass-size eParticipation political initiative recently founded by private citizens. The use of OCs is a common strategy to involve groups of people to easily connect on-line, cooperating on common and shared interests. We here focus on understanding the internal and external forces influencing on the OCs, to better understand how to manage such OCs within the eParticipation domain. We do so by introducing the concept of tensions, to describe the states that these contrasting forces produce on the OCs, addressing the research question: what tensions occur in OCs for eParticipation? Our work contributes to a deeper understanding of the OCs phenomenon within the eParticipation domain, while also provides avenues for further research.